E 4. Heating Systems Requirements (ADL2 paragraphs 1.24-1.40)
E 4.1 Heating Systems Carbon Intensity Requirement (ADL2 paragraphs 1.25-1.32)
"Heating plant should be reasonably efficient. For heating plant serving hot water and steam heating systems, electric heating and heat pumps (irrespective of the form of heat distribution), a way of complying with the requirement would be to show that:
a) the carbon intensity of the heat generating equipment at the maximum heat output of the heating system is not greater than the value shown in Table 5 column (a) and
b) the carbon intensity of the heat generating equipment when the system is producing 30% of the maximum heat output of the heating system is not greater than the value shown in Table 5 column (b)." (ADL2 paragraph 1.25).
"In order to allow greater design flexibility, there can be a trade-off (in either direction) between the average U-value of the envelope and the carbon intensity of the heating system provided that the rate of carbon emissions is unchanged. A way of complying would be to adjust the average U-value of the building fabric such that it is no worse than the value determined from the following equation:
Ureq = Uref . (εref / εact )
where:
Ureq = the required average U-value.
Uref = the average U-value of the building constructed to the elemental standards of Table 1.
εact = the carbon intensity of the actual heating system at an output of 30% of the installed capacity.
εref = the carbon intensity of the reference heating system at an output of 30% of the installed capacity." (ADL2 paragraph 1.32).
ADL2 paragraph 1.26 implies that a trade-off is permissible on the performance of the system at the maximum heating system output as well as at the 30% output level:
"In some applications electric resistance heating might be appropriate. In such cases the designer will need to improve envelope insulation standards to trade-off against the higher carbon intensity of such forms of heating (see paragraph 1.32).”
This provision can be accommodated by making a small modification to the definition of the adjustment factor for required U-value so that it reads
εref / εact = min(εref100 /εact100, εref30 /εact30 )
where
εact100 , εact30 are the carbon intensities of the actual heating system at 100% and 30% of the installed capacity, and
εref100 , εref30 are the carbon intensities of the reference heating system at 100% and 30% of the installed capacity.
This modification means that if the performance of the actual system relative to the reference system is poorer at 100% than at 30% output the requirement on average U-value is made more stringent, but nonetheless a trade-off is possible on the otherwise uncompromising requirement of paragraph 1.25a.
The Heating Systems analysis performed by the software is based solely on the data entered via the L2 Elemental Heating Systems tab of Part L Building & System data. Results are presented both in the interface and in the Part L results file. Via the Required U-value adjustment factor, the results of this analysis provide an input to the Construction Trade-off Method (see above).
The interface provides facilities for specifying one or more heating systems and describing their characteristics. It also displays the Part L analysis results for the currently defined set of systems.
ADL2 equation (1) provides the basis for the analysis (paragraph 1.27):
ε c = (1/ Σ R ) Σ( R C f / η t )
where
ε c = the carbon intensity of the heating system (kgC/kWh of useful heat)
R = the rated output of an individual element of heat raising plant (kW).
η t = the gross thermal efficiency of that element of heat raising plant (kWh of heat per kWh of delivered fuel).
C f = the carbon emission factor of the fuel supplying that element of heat raising plant (kg of carbon emitted per kWh of delivered fuel consumed) (ADL2 Table 6).
In terms of the inputs entered in the <Virtual Environment> Part L interface, this becomes
ε c = (1/ Σ P ) Σ( P C f / η t )
where
P = the percentage of total building heating at either 30% or 100% maximum heat output.
In the case of heating provided by combined heat and power, the term C f / η t is replaced by ε chp from ADL2 equation (2) (paragraph 1.28):
ε c = Cf / η t – Cdisplaced / HPR
where
η t = the gross thermal efficiency of the CHP engine (kWh of useful heat per kWh of fuel burned)
HPR = the heat to power ratio (kWh of useful heat produced per kWh of electricity output).
C displaced = 0.123 kgC/kWh, the carbon emission factor for displaced grid-supplied electricity.
These equations are used to calculate carbon intensity values for the heat generating equipment working at a) the maximum output of the heating system and b) 30% of the maximum output.
The carbon intensity values are then compared with entries in ADL2 Table 5 to generate a Required U-value adjustment factor based on the performance at maximum output and 30% of maximum output. No pass/fail result is displayed because the values can always be traded off against fabric performance.
ADL2 Table 5 gives maximum allowable carbon intensities at maximum output and 30% of maximum output for: 1. Natural gas, 2. Other fuels. In cases where more than one heating fuel is used, an average of the values in Table 5 is used, weighted by system output at maximum output or 30% maximum output as appropriate.
E 4.2 Heating Controls Requirements (ADL2 paragraphs 1.33-1.37)
"The building should be provided with zone, timing and temperature controls such that each functional area is maintained at the required temperature only during the period when it is occupied..." (ADL2 paragraph 1.33).
"Hot water should be provided safely, making efficient use of energy and thereby minimising carbon emissions..." (ADL2 paragraph 1.35).
These requirements cannot be analysed in software but are included for completeness.
E 4.3 Insulation of Pipes, Ducts & Vessels Requirement (ADL2 paragraphs 1.38-1.40)
" A way of meeting the requirement would be to apply insulation to the standards required in BS 5422 to all pipework, ductwork and storage vessels..." (ADL2 paragraph 1.39).
These requirements cannot be analysed in software but are included for completeness.
E 5. Lighting Systems Requirements (ADL2 paragraphs 1.41-1.59)
"Lighting systems should be reasonably efficient and make effective use of daylight where appropriate..." (ADL2 paragraph.1.41).
Lighting system requirements are not analysed by the current Part L software implementation.
E 6. Air-conditioning and Mechanical Ventilation (ACMV) Requirement (ADL2 paragraphs 1.60-1.68)
"Buildings with ACMV should be designed and constructed such that:
a) the form and fabric of the building do not result in a requirement for excessive installed capacity of ACMV equipment...
b) components such as fans, pumps and refrigeration equipment are reasonably efficient and appropriately sized...
c) suitable facilities are provided to manage, control and monitor the operation of the equipment and the systems." (ADL2 paragraph.1.61).
